The industry’s anti-fraud initiative for online advertising has finally and officially made its way to OTT and mobile in-app advertising. On March 13, the Interactive Advertising Bureau Tech Lab released the final version of app-ads.txt, which is intended to combat bad actors that disguise themselves as another company’s app in order to siphon the money that advertisers are spending on mobile and OTT advertising. App-ads.txt bears many similarities to the original ads.txt, but there is a crucial difference that could complicate advertisers’, publishers’ and ad tech vendors’ efforts to adopt the initiative.

I think I knew ads.txt. But WTF is app-ads.txt?
It’s the version of ads.txt for mobile in-app and OTT advertising. Mobile and OTT app publishers can list the ad tech vendors that are authorized to sell or resell their ad inventory, and programmatic ad buyers can check these lists to make sure that a company claiming to offer an app’s inventory is actually able to sell the app’s inventory. This way, advertisers can mitigate instances when they think they are buying ads in, say, ESPN’s mobile or OTT app but really are bankrolling fraudsters who see programmatic advertisers are easy marks because of the programmatic supply chain’s historical lack of transparency.

But ads.txt already exists. Why does there need to be a separate version for mobile in-app and OTT advertising?
Two reasons, and they are related. First, app publishers need to publish the lists of their authorized sellers and resellers — these are called app-ads.txt files but they’re formatted the same as ads.txt files — to their websites in order for programmatic buyers to easily access those lists; this is how ads.txt works, and so far it’s worked fine (so long as companies implement it correctly). Second, programmatic ad buyers need to be able to confirm that a list on a publisher’s site corresponds to the app inventory they are trying to buy.

How is an app-ads.txt file able to be associated with a mobile or OTT app?
Through the app listings that app stores publish online. IAB Tech Lab is hoping that app stores will add some HTML code for each app listing that provides the app’s website domain, bundle ID and store ID. The website domain will point to the domain where buyers can find a publisher’s app-ads.txt file online, and the bundle ID and store ID can be matched against the bundle ID and/or store ID that are included in the bid request when an app has an ad impression to sell programmatically.

Why do you say that IAB Tech Lab is hoping that app stores will add that code?
Because most have not. App store support was a major sticking point when app-ads.txt was being developed. Without app store support, there’s no reliable way to ensure that an app-ads.txt file on a publisher’s site corresponds to a given app.

As of right now, several major mobile and OTT app stores, including Apple’s, Amazon’s and Roku’s, do not appear to support app-ads.txt, according to a review of the code for their online app store listings. And Samsung does not appear to publish listings online for apps running on its smart TV platform. Roku declined to comment on future plans, Apple, Amazon and Samsung have yet to answer questions about their plans to support app-ads.txt.

What happens if the other major app stores don’t support app-ads.txt?
A lot of headaches. First off, it depends if an app store publishes app listings online. If it doesn’t, then basically app-ads.txt won’t work for those apps. If an app store does publish app listings online — as Apple, Amazon and Roku do — then it depends on whether those online app store listings include the website URL of the app’s publisher. Apple and Amazon include publisher’s website URLs in their app store listings. Roku does not appear to do so, but its online app listings do feature links to the privacy policy on a publisher’s site, which could be used to find the publisher’s app-ads.txt file if that file is hosted on the same domain. In each case, the companies developing tools to check for app-ads.txt files will need to tweak those tools for each app store to find publishers’ URLs, and publishers will need to ensure those URLs match the domains that host their app-ads.txt files.

So it will probably take a while for publishers, advertisers and vendors to adopt app-ads.txt, just like with ads.txt?
Yup.